Hashmap get function returns null

问题

I have a hashmap which is

public HashMap<String, ArrayList<Integer>> invertedList;

I show you my invertedList in watch list during debugging:

invertedList.toString(): "{ryerson=[0, 2, 3], 23=[3], award=[1], andisheh=[0, 2]}"

In the same watch list when I enter:

invertedList.get("ryerson")

I get null as result, also in the code. As you can see "ryerson" is already there as a key in my invertedList and I should get [0, 2, 3] as a result!!! What is happening here? I'm so confused!

I know there is a problem with ArrayList as values, because I tested Integer as values and it worked fine, but still don't know how to solve it. I am new to java, used to work with C#.

The complete code of invertedList:

public class InvertedIndex {
public HashMap<String, ArrayList<Integer>> invertedList;
public ArrayList<String> documents; 
public InvertedIndex(){
    invertedList = new HashMap<String, ArrayList<Integer>>();
    documents = new ArrayList<String>();
}
public void buildFromTextFile(String fileName) throws IOException {
    FileReader fileReader = new FileReader(fileName);
    BufferedReader bufferedReader = new BufferedReader(fileReader);
    int documentId = 0;
    while(true){
        String line = bufferedReader.readLine();
        if(line == null){
            break;
        }
        String[] words = line.split("\\W+");
        for (String word : words) {
            word = word.toLowerCase();
            if(!invertedList.containsKey(word))
                invertedList.put(word, new ArrayList<Integer>());
            invertedList.get(word).add(documentId);

        }
        documents.add(line);
        documentId++;
    }
    bufferedReader.close();
}

The test code:

@Test
public void testBuildFromTextFile() throws IOException {
    InvertedIndex invertedIndex = new InvertedIndex();
    invertedIndex.buildFromTextFile("input.tsv");
    Assert.assertEquals("{ryerson=[0, 2, 3], 23=[3], award=[1], andisheh=[0, 2]}", invertedIndex.invertedList.toString());      
    ArrayList<Integer> resultIds =  invertedList.get("ryerson");
    ArrayList<Integer> expectedResult = new ArrayList<Integer>();
    expectedResult.add(0);
    expectedResult.add(2);
            expectedResult.add(3);
    Assert.assertEquals(expectedResult, resultIds);
}

The first Assert works fine, the second one, resultIds is null.

回答1:

If I'm reading this right, and assuming correctly, this test function is inside the InvertedIndex class. I only make that assumption because the line

ArrayList<Integer> resultIds =  invertedList.get("ryerson");

should actually be uncompilable as there is no local variable called "invertedList".

That line should read

ArrayList<Integer> resultIds =  invertedIndex.invertedList.get("ryerson");

回答2:

Your first assert tests the value of invertedIndex.invertedList. The second one gets a value from invertedList, and not from invertedIndex.invertedList. You've probably defined a map with the same name in your test, which is different from the one used by invertedIndex.

来源：https://stackoverflow.com/questions/22489756/hashmap-get-function-returns-null

标签

java

get

null

hashmap